Middle Pleistocene marine deposits on the Kola Peninsula (NW Russia)

摘要

A unique Middle to Late Pleistocene site is situated in the southern part of the Kola Peninsula on the right bank of the lower Varzuga River, providing for the first time valuable evidence concerning Middle Pleistocene climate change and a marine transgression event during this period. The corresponding strata are exposed in a 2-km-long natural outcrop traceable along the abrupt slope of the river valley where the fluvial erosion and slumping have dissected a remnant elongated hill. Middle Pleistocene marine deposits compose here the basal part of the sedimentary succession. Lithological, sedimentological and structural field study accompanied by ESR dating of mollusc shells taken from marine sediments and a detailed palynological investigation have been carried out.The basal part of the Varzuga section is represented by superposition of consolidated clay, loam, sandy loam with subfossil mollusc shells, and small lenses of coarse-grained sand, and pebbles (Unit 1). Marine shells were ESR dated between 319.0 +/- 38.5 ka and 316.0 +/- 23.6 ka. Glacial diamicton and glacifluvial sands (Unit 2), probably also Middle Pleistocene in age, overlay the marine sediment with sharp contact. The uppermost part of the sequence consists of the Late Pleistocene marine sediments, glacial diamicton, glacifluvial sand, and presumably Late Glacial and early Holocene lacustrine deposits. One hundred samples of marine (Unit 1) and lowermost part of glacial (Unit 2) deposits were palynologically reinvestigated. On the basis of detailed palynostratigraphy, 19 pollen assemblage zones were identified. Recurring vegetative assemblages characterized by increasing quantity of Betula with occurrence of mesophilous and thermophilous components (Alnus, Quercus, Tilia, Ulmus, Carpinus, Corylus, Osmunda, Nuphar, Nymphaea) indicate five Middle Pleistocene warm events, mostly during Marine Isotope Stage (MIS) 9.